1. Field of the Invention
The present invention is directed generally to an electromagnetic relay having a coil which includes a winding applied to a coil member between end flanges thereof and having a core axially arranged within the winding. A yoke is included arranged outside of the winding and connected to one end of the core. An armature is seated at the yoke and forms a working air gap with the free end of the core. At least one switch contact is actuateable by the armature, the switch contact being connected through a power lead element to a terminal element, whereby the power lead element is conducted at least once through the excitation flux circuit formed by the yoke, core, and the armature.
2. Description of the Related Art
When switching electromagnetic load relays, a problem occurs in specific applications in that the excitation voltage for the winding drops off during the attraction of the armature. As a result, the armature is no longer fully attracted under certain circumstances which causes the armature to undergo a chattering motion. This causes the switch contact to either not close or to undergo repeated interruptions or openings before closing. This problem occurs particularly often in applications where the voltage source for the excitation winding of the relay also simultaneously supplies the current to the load, as is specifically the case in motor vehicles. When certain users or loads, such as lamps or starters, are switched on in a motor vehicle, extremely high turn-on current peaks appear which leads to the reduction of the battery voltage. Thus, reliable operation of the relay is no longer assured.
Another, related problem occurs when relays are driven by mechanical switches which have multiply longer bouncing times for the switch elements. As a result of these bouncing impacts, the relay is then also multiply switched on and off until it ultimately closes. Particularly when extremely high turn-on current peaks are required by the load, this leads to great stressing and/or erosion of the relay contacts. In extreme cases, for example, when switching lamp currents, it leads to welding of the contact members.
In a relay disclosed in European Published Application 0 231 793 and corresponding U.S. Pat. No. 4,803,589, it is provided to conduct the load current between the coil and yoke so that an auxiliary excitation is induced isodirectionally with the excitation of the winding. Given appropriate dimensioning, a reliable response of the relay is guaranteed in this way even when the excitation voltage drops off during the turn-on event or is interrupted in the interim as a consequence of a bouncing switch.
Given a relay of small volume, however, problems arise for guiding the load current around the excitation flux circuit under certain circumstances when there is only an extremely small gap present between the winding and the yoke, so that it is only possible to conduct a power lead element of large cross section therethrough with difficulty. It has thereby also been proposed to conduct a thin plate which occupies essentially the entire length of the winding between the winding and the yoke as the power lead element in order to obtain the required cross section for the load current and still provide an optimally low height. In any case, however, problems derive during assembly and problems derive in view of the insulation between the load circuit and winding in this type of relay.